1. Field of the Invention
The present invention relates to orthopedic braces.
2. Description of the Related Art
FIG. 1 illustrates a conventional orthopedic knee brace 30. Such braces tend to slide downward on the wearer's leg 32. A few different factors cause this downward migration. First, when the wearer is standing or sitting gravity tends to pull the brace 30 downward along the wearer's leg 32. When the wearer walks or runs, the added acceleration of the wearer's gait exacerbates the downward pull of gravity upon the brace 30.
Second, like the illustrated brace 30 most knee braces are secured to the wearer's leg 32 with straps 34. These straps 34 generate friction on the leg 32 by applying a compressive force to the leg 32. But the human leg 32 has a generally conical shape, being wider at the thigh 36 and narrower at the calf 38. As a result, the compressive force applied by each strap 34 tends to make the strap 34 slide downward. Further, the conical shape provides no resistance to the natural tendency of the brace 30 to slide downward under the influence of gravity.
Third, conventional straps 34 do not contact the wearer's leg 32 at all points around the perimeter. As FIG. 2 illustrates, ends of the straps 34 attach to outward facing surfaces 39 of rigid frame portions 40 of the brace 30. The outward facing surfaces 39 of the frame portions 40 are spaced from the wearer's leg 32. This spacing creates gaps 42 between the straps 34 and the medial regions 44 and lateral regions 46 of the wearer's leg 32, where the straps 34 connect to the frame 40. The gaps 42 create uneven pressure on the leg 32, with pressure points at the anterior regions 48 and posterior regions 50. The arrows in FIG. 2 represent the pressure applied by the straps 34, with the magnitude of the pressure being directly proportional to the length of the arrow. The pressure points and gaps 42 contribute to wearer discomfort and the tendency for the straps 34 to slide down the leg 32.
To combat downward migration, some knee braces include a strap that resides on the top of the wearer's gastroc muscle 52 (FIG. 1). For example, the brace 30 illustrated in FIG. 1 includes such an anti-migration strap 34. FIGS. 9-12 of U.S. Pat. No. 4,643,176 also disclose an anti-migration strap 60. The strap 60 is constructed of a flexible but substantially non-stretchable material. The strap 60 wraps around the wearer's leg where the calf flares outwardly immediately below the knee joint.
In certain knee braces, particularly those knee braces that treat and/or prevent injuries to the wearer's anterior cruciate ligament (ACL), an anti-migration strap atop the gastroc muscle can hinder the intended beneficial function of the orthosis. FIG. 3 illustrates the shear forces F1, F2 that a knee brace should apply to a wearer's leg 32 in order to simulate the action of the ACL (see, for example, U.S. Pat. No. 4,697,583). FIG. 4 illustrates an ACL brace 30 including an anti-migration strap 34 atop the gastroc muscle 52. FIG. 4 further illustrates the direction of each force F1, F2, F3 applied by each strap 1, 2, 3. The straps 1, 2 apply beneficial forces F1, F2, while the strap 3 applies a force F3 that opposes the force F2 applied by the strap 2.
A system for comfortably fitting an orthopedic brace to a wearer's limb while effectively preventing migration of the brace and without hindering the intended function of the brace would be of great benefit to those who wear orthopedic braces.